// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
//
// WriteBatch::rep_ :=
//    sequence: fixed64
//    count: fixed32
//    data: record[count]
// record :=
//    kTypeValue varstring varstring          |
//    kTypeDeletion varstring
// varstring :=
//    len: varint32
//    data: uint8[len]

#include "leveldb/write_batch.h"

#include "db/dbformat.h"
#include "db/memtable.h"
#include "db/write_batch_internal.h"
#include "leveldb/db.h"
#include "util/coding.h"

namespace leveldb {

// WriteBatch header has an 8-byte sequence number followed by a 4-byte count.
static const size_t kHeader = 12;

WriteBatch::WriteBatch() { Clear(); }

WriteBatch::~WriteBatch() = default;

WriteBatch::Handler::~Handler() = default;

void WriteBatch::Clear() {
    rep_.clear();
    rep_.resize(kHeader);
}

size_t WriteBatch::ApproximateSize() const { return rep_.size(); }

Status WriteBatch::Iterate(Handler* handler) const {
    Slice input(rep_);
    if (input.size() < kHeader) {
        return Status::Corruption("malformed WriteBatch (too small)");
    }

    input.remove_prefix(kHeader);
    Slice key, value;
    int found = 0;
    while (!input.empty()) {
        ++found;
        char tag = input[0];
        input.remove_prefix(1);
        switch (tag) {
        case kTypeValue:
            if (GetLengthPrefixedSlice(&input, &key) &&
                GetLengthPrefixedSlice(&input, &value)) {
                handler->Put(key, value);
            } else {
                return Status::Corruption("bad WriteBatch Put");
            }
            break;
        case kTypeDeletion:
            if (GetLengthPrefixedSlice(&input, &key)) {
                handler->Delete(key);
            } else {
                return Status::Corruption("bad WriteBatch Delete");
            }
            break;
        default:
            return Status::Corruption("bad WriteBatch tag");
        }
    }
    if (found != WriteBatchInternal::Count(this)) {
        return Status::Corruption("WriteBatch has wrong count");
    } else {
        return Status::OK();
    }
}

int WriteBatchInternal::Count(const WriteBatch* b) {
    return DecodeFixed32(b->rep_.data() + 8);
}

void WriteBatchInternal::SetCount(WriteBatch* b, int n) {
    EncodeFixed32(&b->rep_[8], n);
}

SequenceNumber WriteBatchInternal::Sequence(const WriteBatch* b) {
    return SequenceNumber(DecodeFixed64(b->rep_.data()));
}

void WriteBatchInternal::SetSequence(WriteBatch* b, SequenceNumber seq) {
    EncodeFixed64(&b->rep_[0], seq);
}

void WriteBatch::Put(const Slice& key, const Slice& value) {
    WriteBatchInternal::SetCount(this, WriteBatchInternal::Count(this) + 1);
    rep_.push_back(static_cast<char>(kTypeValue));
    PutLengthPrefixedSlice(&rep_, key);
    PutLengthPrefixedSlice(&rep_, value);
}

void WriteBatch::Delete(const Slice& key) {
    WriteBatchInternal::SetCount(this, WriteBatchInternal::Count(this) + 1);
    rep_.push_back(static_cast<char>(kTypeDeletion));
    PutLengthPrefixedSlice(&rep_, key);
}

void WriteBatch::Append(const WriteBatch& source) {
    WriteBatchInternal::Append(this, &source);
}

namespace {
class MemTableInserter : public WriteBatch::Handler {
public:
    SequenceNumber sequence_;
    MemTable* mem_;

    void Put(const Slice& key, const Slice& value) override {
        mem_->Add(sequence_, kTypeValue, key, value);
        ++sequence_;
    }
    void Delete(const Slice& key) override {
        mem_->Add(sequence_, kTypeDeletion, key, Slice());
        ++sequence_;
    }
};
} // namespace

Status WriteBatchInternal::InsertInto(const WriteBatch* b, MemTable* memtable) {
    MemTableInserter inserter;
    inserter.sequence_ = WriteBatchInternal::Sequence(b);
    inserter.mem_ = memtable;
    return b->Iterate(&inserter);
}

void WriteBatchInternal::SetContents(WriteBatch* b, const Slice& contents) {
    assert(contents.size() >= kHeader);
    b->rep_.assign(contents.data(), contents.size());
}

void WriteBatchInternal::Append(WriteBatch* dst, const WriteBatch* src) {
    SetCount(dst, Count(dst) + Count(src));
    assert(src->rep_.size() >= kHeader);
    dst->rep_.append(src->rep_.data() + kHeader, src->rep_.size() - kHeader);
}

} // namespace leveldb
